I have a client in my network which it has 2 NIC, assume eth0 and eth1. A specific scanner with ip address of 192.168.1.1 is connected to eth0 of this client and eth1 is connected to my network. In my network i have a specific printer with ip address of 192.168.1.80. The problem is when i tried to send request for printing to ip address 1.80 from this client, nothing happened unless i disconnect my scanner from client eth0! What cause such problem and how can i fix that?
Apparently you have the same networks 192.168.1.0/24 attached to both of your interfaces, butr they are not physically the same. If you cannot alter the address of the scanner network, you need the routing to be specific enough. For example, if your eth0 address is 192.168.1.2/30 and your eth1 address is 192.168.1.4/24 the more specific route via eth0 will only be taken for 192.168.1.0 up to 192.168.1.3. This is still a mess because likely the scanner still has the /24 mask and you still cannot contact 192.168.1.0 up to 192.168.1.3 of the eth1 net, but this may be a (I say it again: horrible) workaround.
Another (just as horrible) workaround would be to add a specific host route to 192.168.1.80 via eth1 (I'm somewhat confuse because you tagged this as Windows but use Linux-like NIC names, so I don't add the specific routing command)